1. Field of the Invention
This invention relates to retrievable packers for use on top of gravel packed screen liners and methods of use thereof, and more particularly, to a packer attachable to a liner screen and a method which eliminates excessive slip drag during setting of a packer element thereof and which utilizes pressure from below the packer to further engage the slips.
2. Description of the Prior Art
Use of packers above gravel packed liner screens is known in the art. Typically, the liner screen is at the bottom of a tool string, releasbly disposed at a point below a gravel packer. After the gravel packing operation, the gravel packer is unset, and the tool string is detached from the liner screen. The gravel pack keeps the liner screen positioned while the tool string is removed from a well. A packer, frequently referred to as a tieback packer, is run into the well bore and set above the liner screen in the gravel pack. The tieback packer is then released from the tool string, and the tool string again removed from the hole.
Many such packers utilize slips to hold the packer in position when the packer element is sealingly engaged with the well bore. However, a problem with current packers is that the slips are dragged along the well bore during the setting process. The result is that the slips are difficult or impossible to disengage from the well bore when it is desired to retrieve the packer. In such cases, the packer may have to be milled over, an expensive and time-consuming process.
The tieback packer of the present invention solves these problems in that it eliminates excessive slip drag by the slips on the well bore during setting by using a spring for preventing downward motion of the tool string from exerting excessive force on the slips. After the packer element is set, pressure from below the packer forces a wedge portion thereof under the slips, setting them tighter. In this way, the slips are securely set without excessive drag.
A bridge plug having a force limiting spring is shown in Halliburton Services Catalog No. 41, pages 4027 and 4028, and Halliburton Tools Manual, pages 2-43, 2-51 and 2-52. A production packer utilizing a spring for engaging slips is disclosed in U. S. Pat. No. 3,584,684 to Anderson et al., and assigned to the assignee of the present application. Unlike the tieback packer of the present invention, these prior apparatus require rotation during a setting operation.
No rotation is necessary for setting the slips or packer element in the present invention. Simple longitudinal movement of the tool string is used to set and release the slips and packer element.